The present invention relates to an image forming device comprising a fixing device for heat-fixing a formed unfixed image of a toner image and the like, in a copying machine, laser beam printer and the like using an electrophotograph method.
The image forming device utilizing an electrophotograph method creates a manifest image by powder toner from a latent image formed on a photosensitive body having a photosensitive layer which works as a recording medium, and transfers said manifested toner image onto a sheet-type paper which is the image holding body, and since said toner is unfixed, heat is applied to melt the toner, and then pressure is added thereto to fix said toner image onto the paper. In order to do so, a fixing device is provided on the lower stream side of a paper conveyance passage which passes through an image forming region, for example, just before a discharge portion of the paper.
As one example of such fixing device, a fixing device is formed of a heat roll having in the interior thereof a heater lamp comprising a halogen lamp as the heating source, and a pressurization roll pressurized to said heat roll by a predetermined pressurization force.
The fixing device is positioned in front of a discharge portion opening to the exterior of the conveyance passage which passes through an image forming portion, wherein a toner image on a sheet-type paper formed at the image forming portion is contacted to the heat roll, and by the heat of the heat roll and the pressurization force provided in co-operation with the pressurization roll, the toner image is heat-fixed to the sheet.
The heat roll comprised in the fixing device is equipped with the heater lamp positioned inside a cylinder having a pipe of aluminum (Al) as a cored bar, the cylinder surface being covered by a silicon rubber member and the like having a good releasing character against the toner and the like. The silicon rubber covering layer and the cored bar are adhered and fixed together by an adhesive called a primer, thereby forming the heater roll.
The surface of the heat roll is maintained at a fixable temperature, in order to heat-fix said toner to the sheet of paper. Therefore, a heat detection sensor such as a thermistor is mounted so as to contact the surface of the heat roll, and in response to the heat detection signal from the sensor, the driving control of the power supply for the heater lamp is operated, and the heat roll surface temperature is maintained at a set temperature enabling fixing operation.
Further, the pressurization roll is forced toward the heat roll by a pressurization lever so as to press the paper to the heat roll direction. The pressurization lever is axially supported on one end, and the other end is forced by a spring so as to pressurize the roll toward the heat roll.
If the toner image is not single colored, but rather a colored image where a plurality of colors are superposed, then toner may easily be adhered to the heat roll, causing an offset where the adhered toner is transferred to the next sheet of paper. Therefore, in order to remove the toner adhered to the heat roll, a cleaning means is provided. The cleaning means either presses a cleaning pad, or a cleaning web, onto the roll surface, so as to wipe off the adhered toner on the heat roll.
Moreover, in order to prevent toner from adhering to the heat roll surface, an application device for applying to the heat roll surface an oil having good releasing ability against toner, such as silicon oil, is further equipped. The application device comprises an application roll for applying oil to the heat roll surface, an oil tank for storing the oil of an offset preventing liquid, a supply felt for supplying the oil in the oil tank to the application roll surface, and a blade for uniforming the oil supplied to the application roll.
The felt for supplying oil is submerged at one end to the oil inside the oil tank, and the other end of the felt is pressurized by a forcing means of spring and the like so as to contact the application roll. The oil supplied to the rotating application roll is flattened uniformly by the blade, and by rotating with contact to the heat roll, a uniform oil layer could be applied to the heat roll surface.
The fixing device having the above mentioned structure is formed as a unit and mounted removably to the image forming device body. Therefore, each of the above-mentioned members are stored inside a casing so as to form one unit. On the casing is formed an opening for introducing the paper to the pressurizing portion between the heat roll and the pressurization roll, and a discharge exit for discharging the fixed paper.
Further, in correspondence to the opening, a guide for guiding the paper to rollers, and a positioning hole for positioning the unit of the fixing device to the predetermined position in the image forming device body are formed to the casing.
On the mounting stage for fixing the fixing device to the predetermined position on the image forming device body is formed a positioning pin for insertion to the positioning hole. The casing forming the fixing device unit is further equipped with a fixed piece for fixing the fixing device to the mounting stage, and a fixing piece formed on the mounting stage. The two pieces are fixed by a fixing screw.
In the fixing device formed as one unit, when the paper is jammed at that position, a part of the image forming device is opened, and the fixing state between the mounting stage is released, or in other words, the fixing screw is removed, and the fixing device is taken out by the whole unit. Thereafter, the pressurized state of the heat roll and the pressurization roll is released. The release structure works so as to remove the pressure by rotating the pressurization lever against the force of the spring. Thereby, the jammed paper could be removed easily.
According to the fixing device formed as a unit, it is mounted removably to the image forming device body so as to simplify the jam management and the like, thereby considering easy maintenance for the user. Moreover, the fixing device has a shorter life than the fixing device body, and the general removable structure enables easy replacement. In other words, in order to improve the serviceability and the operability (operational characters), the fixing device is mounted removably to the image forming device body.
In the conventional jam management, when jam was sensed, the action of the fixing device was also stopped in response, and the jammed paper was removed by pulling out the paper in the conveyance direction. Such operation fixes the toner image utilizing the remaining heat of the heat roll, thereby preventing the contamination of the image forming device interior or the user by the unfixed toner. In this case, when the jammed paper could not be pulled out, as was explained above, the pressurization force on the pressurization roll is released.
As was disclosed above, the conventional fixing device was considered to pull out the jammed paper to the paper conveyance direction in order to solve the fouling caused by the unfixed toner, thereby improving the serviceability and the operability of the jam management. In other words, the unfixed toner image is fixed to the paper by the remaining heat of the heat roll in the fixing device.
However, in the fixing device, the providing of electricity to the heater lamp in the heat roll is also released when the jam has occurred, so therefore, the fixing of the unfixed toner may not always be performed completely merely by the use of remaining heat of the heat roll. Moreover, when the toner image is a colored one, the fixing performance may be very unfavorable, and the paper may be pulled out in a unfixed state, causing fouling by the toner.
Since sufficient fixing is not performed, a cold offset may occur where the toner adheres to the heat roll. Therefore, the load of the cleaning means for removing the toner is increased, causing cleaning disorder. Then, an offset may occur where the toner is transferred to the paper after the jam management.
Moreover, if the pressure of the pressurization roll is released when pulling out the jammed paper, because sufficient pressurization status will not be maintained, and fixing disorder of the unfixed toner image may occur, making remarkably the above mentioned problems. Even further, the unfixed toner may be dispersed when pulling out the paper, fouling not only the fixing device but also the user or other components. In this case, when the toner contaminates the application felt preventing offset, it may cause an uneven application of oil, and stable fixing could no longer be performed.
In order to completely remove the toner adhered to the heat roll, a web method-type cleaning means is effective. However, this method causes complication of the structure, increasing the size of the fixing device and the cost. Further disadvantage of the method is the occurrence of oil lines on an OHP sheet.
Therefore, by taking the fixing device out of the image forming device body when removing the jammed sheet, the unfixed toner will not foul the interior of the image forming device. However, in order to remove the fixing device, the fixing screw working as the fixing means must be removed, and further, the pressure on the pressurization roll must be released. The operation may become complex, and when the user forgets to release the pressure, the removal of the jammed paper may be difficult, or unfixed toner may be dispersed by the removing operation, fouling the user.